The present invention relates to a heat exchanger having sheet-metal plates in spaced pairs, each pair having rail-like spacers or cleats between laterally outer parallel longitudinal edges of the plates to keep them at fixed spacing from each other and to define, in each case, a flat inner flow passage between the plates, there being at least two systems of flow passages, and at least some of the flow passages being of U-shaped cross-section.
Prior art heat exchangers of the character indicated and having rail-like spacers of continuously rectangular cross-section are known from West German utility model (Gebrauchsmuster) No. 1,928,039. Such heat exchangers have the advantage that they can be very easily manufactured by stacking solder-clad metal sheets one above the other in sandwiching relation with interposed rail-like spacers, the sandwiched unit being then placed in a soldering bath or in a soldering oven where the parts then "bake together" to produce a solder-consolidated unit.
Heat exchangers of this kind, when applied, for example, as air/air coolers, find preferred use as intermediate coolers and as after-coolers for compressors, or as supercharged-air coolers for supercharged engines. When used as oil/air coolers, they may serve as oil coolers for screw-type compressors, hydraulic systems or the like, and as lubricating-oil coolers for internal combustion engines or other apparatus having a lubricating-oil circuit which is subjected to heat. In all of the indicated applications, it is desirable that the cooler be of least possible weight. This is particularly important in the case of coolers which are flanged on one side for mounting to an associated engine block, and where the rotational moment of inertia of the cooler must not exceed a given value.
Coolers of the aforementioned type in which the rail-like spacers are of U-shaped profile, with a U-shaped cross-section extending over their entire length, have been known since the turn of the century, namely, from French Pat. No. 350,382 and, later on, French Pat. No. 1,544,973. Using such U-shaped spacers, the weight of the heat exchanger can be reduced only at the expense of its strength; such U-shaped spacers are out of the question in any case in which elevated pressures and/or elevated external mechanical loads are to be expected.